1. Field of the Invention
The present invention relates to a stator structure of a claw pole stepping motor and, more particularly, to an improvement in performance, and reduction in diameter and production cost attained by improvement in construction of the stator.
2. Description of the Prior Arts
Recently, remarkable progress has been made for various devices in performance and particularly in miniaturization. Accordingly, various devices have adopted a plurality of specific motors as required for their functions. Stepping motors are best suited in particular for requirement of positioning control. However, they have not been adopted due to limitations on the miniaturization of motors.
FIG. 1A is a partly sectional perspective view showing a stator structure of a conventional claw-pole stepping motor, and FIG. 1B is an enlarged perspective view showing pole teeth of the stator structure.
Referring to FIG. 1A, a motor is mounted on an upper flange 1 and an outer yoke 2 has, at the inner circumference thereof, pole teeth 4 that are made of a soft magnetic steel plate processed by sheet metal working. An inner yoke 3 also has, at the inner circumference thereof, pole teeth 4 that are made of a soft magnetic steel plate processed by sheet metal working. The yokes 2 and 3 are arranged such that a coil 6 with magnetic wires wound around a bobbin 5 is arranged therebetween and that the pole teeth 4 provided at the inner circumference of the yokes 2 and 3 face are combined with each other to constitute a pancake 15. Two pancakes 15 each with the yokes 2 and 3 and the coil 6 thus arranged are positioned back to back to constitute a stator. The outer yoke 2 of the lower pancake 15 as shown is provided with a lower flange 7 with a bearing 8 arranged at the center thereof. A sleeve 10 connects a rotor magnet 9 to a shaft 11 that provides the rotation center of the rotor.
FIG.2 is a cross-sectional view showing the pancake of the claw pole stepping motor shown is FIG. 1A.
Particularly referring to the structure of the pole teeth 4 in the pancake 15 shown in FIG.2, it will be understood that the pole teeth 4 are subject to stress caused by a sheet metal working process, and are thin in thickness, because the pole teeth 4 are formed by such process at the inner circumference of the yokes 2 and 3, respectively. Accordingly, the pole teeth 4 are liable to develop warping or bending as well.
As mentioned in the foregoing, a claw pole stepping motor has yokes 2, 3, and the pole teeth 4 manufactured in unitary structure. The smaller the diameter of the motor, the thinner the thickness of the material plate needed to secure a space for the coils and workability, and the shorter the height of the pole teeth as well. This might cause manufacturing difficulty and degradation of motor characteristics as well, thereby resulting in limiting the reduction in the diameter up to an outer diameter of 8 mm. This has resulted in provision of an encoder as a position detector in a DC motor for positioning control which results in an extremely expensive structure. However, considering the current environment regarding stepping motors, high-performance magnets such as the rare earth magnet have been developed for use in rotor magnets facing stators. This has laid the cornerstone for possibly improving the characteristics of the motor only if the stators can be worked properly and thus raised requirements for an appropriate method for manufacturing the stator.